(a) Field
The disclosed technology relates to a circuit capable of expanding a hold-up time, and a converter including the same.
(b) Description of the Related Technology
An input terminal of a converter is connected to ac-rectifying circuit of which an ac input is rectified and dc is supplied, or an output of a power factor compensation circuit.
When the voltage of the ac-rectifying or the output voltage of the power factor circuit is decreased or blacks out, the output voltage of the converter decreases. A period between a time when the input voltage starts to decrease and a time when the input voltage becomes lower than a threshold voltage is referred to as a hold-up time. The threshold voltage means a minimum input voltage that can constantly maintain the output voltage of the converter.
If the input voltage is less than the threshold voltage, an error operation is generated. For an example, if the input voltage of a half-bridge converter is less than the threshold voltage, a duty of main or auxiliary switches must increase to constantly maintain the output voltage of the half-bridge converter.
However, the maximum duty of the both switches is limited to 50% to prevent short-circuit of the both switches so that the output voltage cannot be maintained constantly during the condition
In an asymmetric half-bridge converter, a duty of the main or auxiliary switch is limited to 50%, but another is not it. If the duty ratio of the switch increases more than 50%, the abnormal operation like that the output voltage rapidly reduces can occur because a voltage conversion ratio of the converter is inverted. For those reasons, the maximum duty of the switches in the topologies is limited.
The input terminal of the converter is connected to a DC link capacitor to smooth the input voltage. To increase the hold-up time, the capacitance of the DC link capacitor must be increased. This causes an increase of the production cost and the circuit size.
The above information disclosed in this background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.